MIAMI: One week after Puerto Ricans approved a measure to become the 51st US state, doubts have begun to emerge over the meaning of the vote and their chances of joining the union.

Residents of the Caribbean island, seized from Spain in 1898, are US citizens, serve in the US military and have US passports, but cannot vote in US presidential elections.

The self-governing US territory's sole representative in Congress is a non-voting delegate in the House of Representatives. However, island residents do not pay federal income taxes.

On November 6 Puerto Ricans were asked two questions in a non-binding vote that critics say was confusing.

First: "Do you agree that Puerto Rico should continue to have its present form of territorial status?" Fifty-two percent of voters answered no, according to official results.

Voters were then given three options: a) Join the United States as a state, b) Become an independent country, or c) Become a "sovereign associated free state," with the terms agreed between the two countries "as sovereign nations."

Voters approved the statehood option by 61 percent -- a move supporters saw as vindication after referenda for statehood failed in 1967, 1993 and 1998.

Not so fast, analysts say.

The main statehood supporter was Governor Luis Fortuno from the New Progressive Party, who lost his re-election bid. Puerto Rico's governor-elect is Alejandro Garcia Padilla, from the pro-status quo Popular Democratic Party.

And if the 33 percent of voters who supported option c) and the five percent who supported independence are added to the 472,000-plus blank votes, "the percentage of people that support statehood drops to 46 percent," said Javier Colon Morera, a political scientist at the University of Puerto Rico.

Ultimately, it's up to the US Congress to decide which territories are allowed into the union.

Confusion over the referendum's wording, along with Fortuno's departure, "will be the most obvious factors" for Congress to ignore the vote, Colon Morera said.

Other obstacles include the Puerto Rican government's deep fiscal debt and the use of Spanish as the official language.

The new state would get two senators, like every other state, and given its population of 3.7 million, it would get five seats in the House of Representatives.

Sparsely populated states like Montana, Wyoming and Alaska all have only one House member, while states like Idaho, New Mexico and West Virginia have three or less.

In Washington, Republican and Democratic staffers told The Hill newspaper that Puerto Rico statehood is unlikely to come up when the next Congress meets in January.

One House aide described the referendum vote to The Hill as a "statistical fiction."